The role of life history parameters as indicators of stock structure

Vital population parameters, such as growth, survival, recruitment, reproduction, distribution, and abundance, are the consequences of life history modes to which fish stocks have evolved. Differences in these parameters have long been used to identify separate management stocks assuming that phenotypic variation is due to genotypic and environmental controls. However, few studies have examined the temporal stability of life history parameters, nor the mechanisms by which differences in these parameters between stocks are maintained. We examine the temporal and spatial stability of several life history parameters of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), and yellowtail flounder (Limanda ferruginea) in the northwest Atlantic Ocean to assess their utility for stock identification. Although significant temporal differences in vital rates were found within stocks, differences were generally maintained between stocks. Both genetic (biological) and oceanographic (physical) conditions play an integral role in maintaining stock structure. Although, the utility of vital life history parameters for stock identification may decrease with stock complexity and exploitation history, their applicability increases with the number of parameters examined. (C) 1999 Elsevier Science B.V. All rights reserved.